The invention relates to a method of forming a tubular member with longitudinal slots in its wall. By way of example, one such tubular member is the tubular shell of a blind breakstem rivet, of the type which is provided with multiple longitudinal slots so that, when the rivet is set by axially compressing part of the shell, the shell deforms into a number of outwardly projecting legs which provide a blind head having a relatively large radial dimension of engagement with the workpiece. Examples of such blind rivets with slotted shells are commercially available under the Registered Trade Marks BULBEX and TLR. However such longitudinally slotted members can be used for many other purposes.
The term xe2x80x98slotxe2x80x99 is intended to include both constructions in which there is a gap between the edges or walls of the parts of the material of the tubular member separated by the slot, and also constructions in which the two edges or walls of the slot are in contact with each other, there being a mechanical discontinuity in the material.
Such slotted members are usually of metal. With a relatively soft metal, such as aluminium, forming the slots in a tubular blank is commonly done by driving through the bore of the blank a close-fitting tool of much harder material, such as steel, which carries a number of radially projecting longitudinal ribs, each having a radial height equal to at least the wall thickness of the tubular blank. Each rib forms a corresponding longitudinal slot in the blank. However, if this method is applied to tubular blanks of steel, it is found that rapid and excessive wear to the tool, particularly to the leading ends of the ribs, occurs.
The present invention aims to provide a new method of forming a tubular member with longitudinal slots in its wall, which overcomes this problem.
Accordingly, the present invention provides, in one of its aspects, a method of forming a tubular member with slots along part of its wall, which method is set out in the accompanying claim 1.
Further features of the invention are set out in the accompanying claims 2 to 16. The invention includes a tubular member which has been formed by a method according to the invention, as set out in claim 16.